With the increasing scarcity of fossil fuels, greater emphasis is being placed on the use of alternative energy sources. One of the most promising alternative energy sources is solar heating. In solar heating radiation is received from the sun and is used to heat a heat transfer medium. The heated heat transfer medium may then be used to store heat for use on demand, e.g., for heating of the home, for supplying hot water for washing, etc.
In the construction of solar heat collectors, it is known that a heat collector may be made more efficient by insulating the enclosure for the heat collector. Thus, it is known to increase efficiency by placing a transparent closure over the enclosure for the heat collector. Solar energy that is received by the heat collector may, thus, pass through the transparent closure to impinge upon a radiant energy absorbing surface, which may be darkened to enhance the absorption of energy by the surface. A heat transfer medium may then be circulated through a conduit placed within the enclosure with the conduit receiving heat from the energy absorbing surface. For example, the energy absorbing surface may be metallic and the conduit may also be metallic. Then, with the conduit in contact with the energy absorbing surface, the absorption of energy may raise the temperature of the surface to convey heat to the conduit by conductive heat transfer. The liquid heat transfer medium circulating within the conduit may then be heated through contact with the heated conduit walls.
A disadvantage in the use of solar heat collectors has involved the narrow range of their functioning capabilities. Previous solar heat collectors have functioned simply by transferring radiant energy to a heat transfer medium, which is used to store the energy. However, during inclement weather, there may not be sufficient solar radiation available to heat up the heat transfer medium within a reasonable time period. Also, if the day is quite dark, the temperature of the stored heat transfer medium may be so high that it would not be possible to provide a temperature differential within the collector which would permit the transfer of heat to the heat transfer medium. Thus, the heat collector may be completely unusable under these conditions.
In increasing the use of solar radiation as an alternative energy source, it would be desirable to provide a heat collector which is more versatile in operation than present solar heat collectors. By way of example, it would be desirable to provide a heat collector which would have several modes of operation, such as a heating mode on the one hand, and a cooling mode on the other. Such a heat collector could be more efficient since the collector could run substantially continuously with the operation of the collector being more or less independent of the whims of weather.
Such a solar heat collector, could, for example, be operated in its heating mode during bright, clear weather with the collector receiving radiant energy at a relatively high intensity level from the sun. However, on overcast days, or during the night time, the heat collector could be operated in its cooling mode. During operation in its cooling mode, the collector could then be used to remove heat from a liquid heat transfer medium with the heat transfer medium being stored in a container to provide a course of chilled liquid for air conditioning and as a sink for heat rejection for heat pumps and other forms of heat engines requiring low temperatures for efficient heat rejection.
A typical example would be to operate during summer months with the collector in the closed mode during the daytime. The hot water collected would be for domestic use and stored in the "hot" tank. During the night, the collector would operate in the open mode and chill water in a "cold" tank. This chilled water would be used during the following daytime hours to assist in cooling the building by circulating the chilled water through the HVAC duct via a fan coil/heat exchanger.